Reference values for pulse oximetry at high altitude

Oxygen saturation reference ranges and factors affecting SpO2 among children living at altitude

AIMS

To determine reference values for oxygen saturation (SpO₂) among healthy children younger than 5 years living at moderately high altitude in Papua New Guinea and to determine other factors that influence oxygen saturation levels.

METHODS

266 well children living at 1810-2630 m above sea level were examined during immunisation clinic visits, and SpO₂ was measured by pulse oximetry. Potential risk factors for hypoxaemia were recorded and analysed by multivariable analysis.

RESULTS

The median SpO₂ was 95% (IQR 93%-97%), with a normal range of 89%-99% (2.5-97.5 centiles). On multivariable analysis, younger children, children of parents who smoked, those asleep and babies carried in bilums, a traditional carry bag made of wool or string, had significantly lower SpO₂.

CONCLUSION

The reference range for healthy children living in the highlands of Papua New Guinea was established. Besides altitude, other factors are associated with lower SpO₂. Some higher-risk infants (preterm, very low birth weight, recurrent acute lower respiratory infection or chronic respiratory problem) may be more prone to hypoxaemia if they have additive risk factors: if parents smoke or they are allowed to sleep a bilum, as their baseline oxygen saturation may be significantly lower, or their respiratory drive or respiratory function is impaired. These findings need further research to determine the clinical importance.

Challenges in the diagnosis of paediatric pneumonia in intervention field trials: recommendations from a pneumonia field trial working group

Pneumonia is a leading killer of children younger than 5 years despite high vaccination coverage, improved nutrition, and widespread implementation of the Integrated Management of Childhood Illnesses algorithm. Assessing the effect of interventions on childhood pneumonia is challenging because the choice of case definition and surveillance approach can affect the identification of pneumonia substantially. In anticipation of an intervention trial aimed to reduce childhood pneumonia by lowering household air pollution, we created a working group to provide recommendations regarding study design and implementation. We suggest to, first, select a standard case definition that combines acute (≤14 days) respiratory symptoms and signs and general danger signs with ancillary tests (such as chest imaging and pulse oximetry) to improve pneumonia identification; second, to prioritise active hospital-based pneumonia surveillance over passive case finding or home-based surveillance to reduce the risk of non-differential misclassification of pneumonia and, as a result, a reduced effect size in a randomised trial; and, lastly, to consider longitudinal follow-up of children younger than 1 year, as this age group has the highest incidence of severe pneumonia.

Is Pulse Oximetry Useful for Screening Neonates for Critical Congenital Heart Disease at High Altitudes?

Now that pulse oximetry is used widely to screen for critical congenital heart disease, it is time to consider whether this screening method is applicable to those who live at high altitudes. Consideration of basic physical principles and reports from the literature indicate that not only is the 95 % cutoff point for arterial oxygen saturation incorrect at high altitudes, but the lower saturations are accompanied by greater variability and therefore there is the possibility of a greater percentage of false-positive screening tests at high altitudes. Because of ethnic differences in response to high altitudes, normative data will have to be collected separately in different countries and perhaps for different ethnic groups.

Adaptation to Life in the High Andes: Nocturnal Oxyhemoglobin Saturation in Early Development

STUDY OBJECTIVES

Physiological adaptation to high altitude hypoxia may be impaired in Andeans with significant European ancestry. The respiratory 'burden' of sleep may challenge adaptation, leading to relative nocturnal hypoxia. Developmental aspects of sleep-related breathing in high-altitude native children have not previously been reported. We aimed to determine the influence of development on diurnal-nocturnal oxyhemoglobin differences in children living at high altitude.

METHODS

This was a cross-sectional, observational study. Seventy-five healthy Bolivian children aged 6 mo to 17 y, native to low altitude (500 m), moderate high altitude (2,500 m), and high altitude (3,700 m) were recruited. Daytime resting pulse oximetry was compared to overnight recordings using Masimo radical oximeters. Genetic ancestry was determined from DNA samples.

RESULTS

Children had mixed European/Amerindian ancestry, with no significant differences between altitudes. Sixty-two participants had ≥ 5 h of nocturnal, artifact-free data. As predicted, diurnal mean oxyhemoglobin saturation decreased across altitudes (infants and children, both P < 0.001), with lowest diurnal values at high altitude in infants. At high altitude, there was a greater drop in nocturnal mean oxyhemoglobin saturation (infants, P < 0.001; children, P = 0.039) and an increase in variability (all P ≤ 0.001) compared to low altitude. Importantly, diurnal to nocturnal altitude differences diminished (P = 0.036), from infancy to childhood, with no further change during adolescence.

CONCLUSIONS

Physiological adaptation to high-altitude living in native Andeans is unlikely to compensate for the significant differences we observed between diurnal and nocturnal oxyhemoglobin saturation, most marked in infancy. This vulnerability to sleep-related hypoxia in early childhood has potential lifespan implications. Future studies should characterize the sleep- related respiratory physiology underpinning our observations.

Respiratory Viral Detections During Symptomatic and Asymptomatic Periods in Young Andean Children

BACKGROUND

Viruses are commonly detected in children with acute respiratory illnesses (ARIs) and in asymptomatic children. Longitudinal studies of viral detections during asymptomatic periods surrounding ARI could facilitate interpretation of viral detections but are currently scant.

METHODS

We used reverse transcription polymerase chain reaction to analyze respiratory samples from young Andean children for viruses during asymptomatic periods within 8-120 days of index ARI (cough or fever). We compared viral detections over time within children and explored reverse transcription polymerase chain reaction cycle thresholds (CTs) as surrogates for viral loads.

RESULTS

At least 1 respiratory virus was detected in 367 (43%) of 859 samples collected during asymptomatic periods, with more frequent detections in periods with rhinorrhea (49%) than those without (34%, P < 0.001). Relative to index ARI with human rhinovirus (HRV), adenovirus (AdV), respiratory syncytial virus (RSV) and parainfluenza virus detected, the same viruses were also detected during 32, 22, 10 and 3% of asymptomatic periods, respectively. RSV was only detected 8-30 days after index RSV ARI, whereas HRV and AdV were detected throughout asymptomatic periods. Human metapneumovirus and influenza were rarely detected during asymptomatic periods (<3%). No significant differences were observed in the CT for HRV or AdV during asymptomatic periods relative to ARI. For RSV, CTs were significantly lower during ARI relative to the asymptomatic period (P = 0.03).

CONCLUSIONS

These findings indicate that influenza, human metapneumovirus, parainfluenza virus and RSV detections in children with an ARI usually indicate a causal relationship. When HRV or AdV is detected during ARI, the causal relationship is less certain.

Overnight Polysomnographic Characteristics and Oxygen Saturation of Healthy Infants, 1 to 18 Months of Age, Born and Residing At High Altitude (2,640 Meters)

BACKGROUND

Approximately 8% of the world population resides above 1,600 m, with about 10 million people living above 2,500 m in Colombia. However, reference values for polysomnography (PSG) and oxygen saturation (Spo2) of children < 2 years old residing at high altitude are currently unavailable.

METHODS

Healthy infants aged 1 to 18 months born and residing at high altitude (Bogotá: 2,640 m) underwent overnight PSG. Four age groups were defined: group 1, < 45 days; group 2, 3 to 4 months; group 3, 6 to 7 months; and group 4, 10 to 18 months. Of 122 children enrolled, 50 had three consecutive PSG tests and were analyzed as a longitudinal subcohort.

RESULTS

A total of 281 PSG tests were performed in 122 infants (56% girls): group 1, 106 PSG tests; group 2, 89 PSG tests; group 3, 61 PSG tests; and group 4, 25 PSG tests. Active sleep diminished and quiet sleep increased with maturation. Apnea-hypopnea indexes (total, central, and obstructive) were highest in group 1 (21.4, 12.4, and 6.8/h total sleep time, respectively) and diminished with age (P < .001). Mean Spo2 during waking and sleep increased with age (P < .001). Nadir Spo2 values during respiratory events were lower in younger infants. Longitudinal assessments of 50 infants confirmed the temporal trends described for the cross-sectional dataset.

CONCLUSIONS

Healthy infants (≤ 18 months old) born and residing at high altitude show preserved sleep architecture but higher apnea-hypopnea indexes and more prominent desaturation with respiratory events than do those living at low altitude. The current study findings can be used as reference values for infants at high altitude.

Cognitive and psychomotor responses to high-altitude exposure in sea level and high-altitude residents of Ecuador

BACKGROUND

High-altitude inhabitants have cardiovascular and respiratory adaptations that are advantageous for high-altitude living, but they may have impaired cognitive function. This study evaluated the influence of altitude of residence on cognitive and psychomotor function upon acute exposure to very high altitude.

FINDINGS

Ecuadorians (31 residing at 0-1,500 m [LOW], 78 from 1,501-3,000 m [MOD], and 23 living >3,000 m [HIGH]) were tested upon their arrival to a hut at 4,860 m on Mount Chimborazo. Cognitive/psychomotor measurements included a go-no-go test (responding to a non-visual stimulus), a verbal fluency test (verbalizing a series of words specific to a particular category), and a hand movement test (rapidly repeating a series of hand positions). Mean differences between the three altitude groups on these cognitive/psychomotor tests were evaluated with one-way ANOVA. There were no significant differences (p = 0.168) between LOW, MOD, and HIGH for the verbal fluency test. However, the go-no-go test was significantly lower (p < 0.001) in the HIGH group (8.8 ± 1.40 correct responses) than the LOW (9.8 ± 0.61) or MOD (9.8 ± 0.55) groups, and both MOD (97.9 ± 31.2) and HIGH (83.5 ± 26.7) groups completed fewer correct hand movements than the LOW (136.6 ± 37.9) subjects (p < 0.001).

CONCLUSIONS

Based on this field study, high-altitude residents appear to have some impaired cognitive function suggesting the possibility of maladaptation to long-term exposure to hypobaric hypoxia.

Feasibility of pulse oximetry screening for critical congenital heart disease at 2643-foot elevation

To evaluate the feasibility of implementing a pulse oximetry screening protocol at a city of mild elevation with a specific focus on the false-positive screening rate. Pulse oximetry screening was performed according to the proposed guidelines endorsed by the American Academy of Pediatrics at a center in Tucson, AZ, at an elevation of 2,643 ft (806 m). During a 10-month period in 2012, 1069 full-term asymptomatic newborns were screened ≥ 24 h after birth. The mean preductal oxygen saturation was 98.5 ± 1.3 % (range 92-100 %), and the mean postductal oxygen saturation was 98.6 ± 1.3 % (range 94-100 %). Of 1,069 patients screened, 7 were excluded secondary to protocol violations, and 1 screened positive. An echocardiogram was performed on the newborn with the positive screen, and it was normal with the exception of right-to-left shunting across a patent foramen ovale. The false-positive rate was 1/1,062 or 0.094 %. The pulse oximetry screening guidelines recommended by the American Academy of Pediatrics are feasible at an elevation of 2,643 ft (806 m) with a low false-positive rate. Adjustments to the protocol are not required for centers at elevations ≤ 2,643 ft. Future studies at greater elevations are warranted.

Increased lung volume in infants and toddlers at high compared to low altitude

Children and adults residing at high altitude (HA) compared to low altitude (LA) have larger lung volumes; however, it is unknown whether this response to chronic hypoxia begins early in life. Our objective was to determine whether infants and toddlers at HA have larger lung volumes compared to infants and toddlers at LA. Oxygen saturation (SaO2 ), functional residual capacity (FRC), as well as serum levels of vascular endothelial growth factor (VEGF) and erythropoietin (EPO) were measured in infants and toddlers from HA (N = 50; 3,440 m) and LA (N = 35; 440 m). There were no significant differences in somatic size for HA and LA subjects; however, HA subjects had significantly lower SaO2 (88.5% vs. 96.7%; P < 0.0001). Subjects at HA had significantly greater FRC compared to subjects at LA (group mean: 209 and 157 ml; P < 0.0001), adjusting for body length. Male infants at HA had a significantly greater FRC compared to males at LA (57 ml; P-value < 0.001); however, the increase in FRC for females at HA compared to LA was not significant (20 ml; P-value = 0.101). VEGF and EPO were significantly higher for subjects at HA compared to LA with no gender differences. In summary, infants and toddlers at HA have lower oxygen saturations, higher serum levels of VEGF and EPO, and higher FRC compared to subjects at LA; however, chronic hypoxia appears to generate a more robust response in lung growth in male compared to female infants early in life.

Respiratory and polysomnographic values in 3- to 5-year-old normal children at higher altitude

STUDY OBJECTIVES

To determine polysomnographic parameter differences in children living at higher altitude to children living near sea level.

DESIGN AND SETTING

Prospective study of non-snoring, normal children recruited from various communities around Denver, CO. In-lab, overnight polysomnograms were performed at a tertiary care children's hospital. All children required residence for greater than one year at an elevation around 1,600 meters.

PARTICIPANTS

45 children (62% female), aged 3-5 years, 88.9% non-Hispanic white with average BMI percentile for age of 47.8% ± 30.7%.

MEASUREMENTS AND RESULTS

Standard sleep indices were obtained and compared to previously published normative values in a similar population living near sea level (SLG). In the altitude group (AG), the apnea-hypopnea index was 1.8 ± 1.2 and the central apnea-hypopnea index was 1.7 ± 1.1, as compared to 0.9 ± 0.8 and 0.8 ± 0.7, respectively, (P ≤ 0.005) in SLG. Mean end-tidal CO2 level in AG was 42.3 ± 3.0 mm Hg and 40.6 ± 4.6 mm Hg in SLG (P = 0.049). The ≥ 4% desaturation index was 3.9 ± 2.0 in AG compared to 0.3 ± 0.4 in SLG (P < 0.001). Mean periodic limb movement in series index was 10.1 ± 12.3 in AG and 3.6 ± 5.4 in SLG (P = 0.001).

CONCLUSION

Comparison of altitude and sea level sleep studies in healthy children reveals significant differences in central apnea, apneahypopnea, desaturation, and periodic limb movement in series indices. Clinical providers should be aware of these differences when interpreting sleep studies and incorporate altitude-adjusted normative values in therapeutic-decision making algorithms.

Reference values for oxygen saturation by pulse oximetry in healthy children at sea level in Chennai

There is little information on oxygen saturation (SaO2) values in children in developing countries.

AIM

To determine the reference values for oxygen saturation by pulse oximetry in healthy children living at sea level in Chennai and aged between 1 mth and 5 yrs.

DESIGN AND SETTING

A prospective study was conducted in Kanchi Kamakoti CHILDS Trust Hospital from February to May 2005.

METHODS

A total of 626 healthy children aged between 1 mth and 5 yrs were examined for heart rate, respiratory rate and SaO2.

RESULTS

The mean SaO2 levels for children in the age groups 1-3 mths, 3 mths to 1 yr, 1-3 years and 3-5 years were 98.5%, 98.8%, 98.9% and 99.1%, respectively. The overall mean and median SaO(2) values for the children in the different age groups were 99%. The mean -2 SD values of oxygen saturation in the age groups were 96.5%, 96.4%, 96.3% and 97.1%, respectively, with an overall mean of 96.6%.

CONCLUSION

The reference value for mean SaO2 in healthy children aged between 1 mth and 5 yrs and living at sea level in Chennai city was 98.5% or more, but the -2SD values had a mean of 96.6%.

The Young Everest Study: preliminary report of changes in sleep and cerebral blood flow velocity during slow ascent to altitude in unacclimatised children

BACKGROUND

Cerebral blood flow velocity (CBFV) and sleep physiology in healthy children exposed to hypoxia and hypocarbia are under-researched.

AIM

To investigate associations between sleep variables, daytime end-tidal carbon dioxide (EtCO2) and CBFV in children during high-altitude ascent.

METHODS

Vital signs, overnight cardiorespiratory sleep studies and transcranial Doppler were undertaken in nine children (aged 6-13 years) at low altitude (130 m), and then at moderate (1300 m) and high (3500 m) altitude during a 5-day ascent.

RESULTS

Daytime (130 m: 98%; 3500 m: 90%, p=0.004) and mean (130 m: 97%, 1300 m: 94%, 3500: 87%, p=0.0005) and minimum (130 m: 92%, 1300 m: 84%, 3500 m: 79%, p=0.0005) overnight pulse oximetry oxyhaemoglobin saturation decreased, and the number of central apnoeas increased at altitude (130 m: 0.2/h, 1300 m: 1.2/h, 3500 m: 3.5/h, p=0.2), correlating inversely with EtCO2 (R(2) 130 m: 0.78; 3500 m: 0.45). Periodic breathing occurred for median (IQR) 0.0 (0; 0.3)% (130 m) and 0.2 (0; 1.2)% (3500 m) of total sleep time. At 3500 m compared with 130 m, there were increases in middle (MCA) (mean (SD) left 29.2 (42.3)%, p=0.053; right 9.9 (12)%, p=0.037) and anterior cerebral (ACA) (left 65.2 (69)%, p=0.024; right 109 (179)%; p=0.025) but not posterior or basilar CBFV. The right MCA CBFV increase at 3500 m was predicted by baseline CBFV and change in daytime SpO2 and EtCO2 at 3500 m (R(2) 0.92); these associations were not seen on the left.

CONCLUSIONS

This preliminary report suggests that sleep physiology is disturbed in children even with slow ascent to altitude. The regional variations in CBFV and their association with hypoxia and hypocapnia require further investigation.

Mean oxygen saturation in well neonates at altitudes between 4498 and 8150 feet

PURPOSE

Examine changes in oxygen saturation in well neonates at altitudes from 4498 to 8150 feet with serial measurements at 12 to 24 hours of age, 36 to 48 hours, and, if still hospitalized, at 60 to 72 hours.

SUBJECTS

Convenience sample of well newborn infants meeting inclusion criteria of normal cardiopulmonary status (centrally pink with adequate perfusion) and no respiratory distress (absence of grunting, retracting, nasal flaring, or tachypnea-respiration ≤ 60/minute).

DESIGN

Nonexperimental, longitudinal, descriptive study.

METHODS

Using Masimo Radical SET monitors the SpO2 values were recorded from infant's right upper extremity to obtain a preductal measurement and then from left lower extremity for postductal measurement at study intervals.

OUTCOME MEASURE

SpO2 values.

RESULTS

The well neonates' birth weights ranged from 1835 to 4740 g [corrected], with 94.3% classified as term and 5.7% classified as preterm. At the data collection intervals based on hours of life, mean SpO2 readings at 4498 feet were 95% to 96.67%, at 6800 feet were 93.91% to 95.36%, at 7851 feet were 91.80% to 94.37%, at 7890 feet were 93.44% to 96.10%, and at 8150 feet were 93.69% to 96.25%. SpO2 readings at sites at or above 6800 feet were significantly lower than those at 4498 feet. No significant differences were noted for sleep state or season. Significant differences were noted in the first and second lower extremity readings between preterm and term neonates, with preterm SpO2 readings higher than term readings.

CONCLUSIONS

Mean oxygen saturation levels for well neonates born at higher altitudes are lower than those born at 4498 feet. Neonates born at or above 6800 feet exhibit "normal" oxygen saturation levels between 91% to 96% rather than the expected 97% found at sea level. These reference values for varying altitudes can guide clinicians to avoid hypoxemia or hyperoxia. If routine oxygen saturation screening for detection of critical congenital heart defects is implemented, these results will provide clinicians the mean values specific for additional altitudes, thus preventing unnecessary interventions when results are lower than the expected 97%.

Pulse oximetry in pediatric practice

The introduction of pulse oximetry in clinical practice has allowed for simple, noninvasive, and reasonably accurate estimation of arterial oxygen saturation. Pulse oximetry is routinely used in the emergency department, the pediatric ward, and in pediatric intensive and perioperative care. However, clinically relevant principles and inherent limitations of the method are not always well understood by health care professionals caring for children. The calculation of the percentage of arterial oxyhemoglobin is based on the distinct characteristics of light absorption in the red and infrared spectra by oxygenated versus deoxygenated hemoglobin and takes advantage of the variation in light absorption caused by the pulsatility of arterial blood. Computation of oxygen saturation is achieved with the use of calibration algorithms. Safe use of pulse oximetry requires knowledge of its limitations, which include motion artifacts, poor perfusion at the site of measurement, irregular rhythms, ambient light or electromagnetic interference, skin pigmentation, nail polish, calibration assumptions, probe positioning, time lag in detecting hypoxic events, venous pulsation, intravenous dyes, and presence of abnormal hemoglobin molecules. In this review we describe the physiologic principles and limitations of pulse oximetry, discuss normal values, and highlight its importance in common pediatric diseases, in which the principle mechanism of hypoxemia is ventilation/perfusion mismatch (eg, asthma exacerbation, acute bronchiolitis, pneumonia) versus hypoventilation (eg, laryngotracheitis, vocal cord dysfunction, foreign-body aspiration in the larynx or trachea). Additional technologic advancements in pulse oximetry and its incorporation into evidence-based clinical algorithms will improve the efficiency of the method in daily pediatric practice.

Oxygen saturation in healthy children aged 5 to 16 years residing in Huayllay, Peru at 4340 m

Hypoxemia is a major life-threatening complication of childhood pneumonia. The threshold points for hypoxemia vary with altitude. However, few published data describe that normal range of variation. The purpose of this study was to establish reference values of normal mean Sao(2) levels and an approximate cutoff point to define hypoxemia for clinical purposes above 4300 meters above sea level (masl). Children aged 5 to 16 yr were examined during primary care visits at the Huayllay Health Center. Huayllay is a rural community located at 4340 m in the province of Pasco in the Peruvian Andes. We collected basic sociodemographic data and evaluated three outcomes: arterial oxygen saturation (Sao(2)) with a pulse oximeter, heart rate, and respiratory rate. Comparisons of main outcomes among age groups (5-6, 7-8, 9-10, 11-12, 13-14, and 15-16 yr) and sex were performed using linear regression models. The correlation of Sao(2) with heart rate and respiration rate was established by Pearson's correlation test. We evaluated 583 children, of whom 386 were included in the study. The average age was 10.3 yr; 55.7% were female. The average Sao(2), heart rate, and respiratory rate were 85.7% (95% CI: 85.2-86.2), 80.4/min (95% CI: 79.0-81.9), and 19.9/min (95% CI: 19.6-20.2), respectively. Sao(2) increased with age (p < 0.001). No differences by sex were observed. The mean minus two standard deviations of Sao(2) (threshold point for hypoxemia) ranged from 73.8% to 81.8% by age group. At 4300 m, the reference values for hypoxemia may be 14.2% lower than at sea level. This difference must be considered when diagnosing hypoxemia or deciding oxygen supplementation at high altitude. Other studies are needed to determine whether this reference value is appropriate for clinical use.

Changing patterns of neuropsychological functioning in children living at high altitude above and below 4000 m: a report from the Bolivian Children Living at Altitude (BoCLA) study

The brain is highly sensitive to environmental hypoxia. Little is known, however, about the neuropsychological effects of high altitude residence in the developing brain. We recently described only minor changes in processing speed in native Bolivian children and adolescents living at approximately 3700 m. However, evidence for loss of cerebral autoregulation above this altitude (4000 m) suggests a potential threshold of hypoxia severity over which neuropsychological functioning may be compromised. We conducted physiological and neuropsychological assessments in 62 Bolivian children and adolescents living at La Paz (∼3700 m) and El Alto (∼4100 m) in order to address this issue. Groups were equivalent in terms of age, gender, social class, schooling, parental education and genetic admixture. Apart from percentage of hemoglobin saturated with oxygen in arterial blood (%SpO(2)), participants did not differ in their basal cardiac and cerebrovascular performance as explored by heart rate, mean arterial pressure, end-tidal carbon dioxide, and cerebral blood flow velocity at the basilar, anterior, middle and posterior cerebral arteries. A comprehensive neuropsychological assessment was administered, including tests of executive functions, attention, memory and psychomotor performance. Participants living at extreme altitude showed lower levels of performance in all executive tests (Cohen effect size = -0.91), whereas all other domains remained unaffected by altitude of residence. These results are compatible with earlier physiological evidence of a transitional zone for cerebral autoregulation at an altitude of 4000 m. We now show that above this threshold, the developing brain is apparently increasingly vulnerable to neuropsychological deficit.

Maternal hemoglobin concentration and pregnancy outcome: a study of the effects of elevation in el alto, bolivia

Iron-deficiency anemia is often under-diagnosed in developing countries, specifically in pregnant populations in regions of high altitude. Hemoglobin levels are not consistently adjusted for elevation, and therefore many anemic patients are left undiagnosed. The purpose of this study was to incorporate current parameters for diagnosing anemia in pregnancy at high altitudes, and to evaluate the effects of appropriately adjusted hemoglobin concentrations on pregnancy outcome. A few studies have examined the effect of elevation on hemoglobin status, and other studies have considered the effects of anemia of pregnancy; however, there is a lack of data demonstrating that altitude-adjusted hemoglobin levels accurately predict pregnancy outcome. Using the Student t-Test, multiple linear regression, and ANOVA statistical analyses, various factors of pregnancy outcome were compared between anemic and non-anemic groups, as defined by hemoglobin cut-off levels adjusted for trimester of pregnancy and altitude. When appropriate adjustments were used, maternal anemia was associated with lower infant Apgar scores at both one minute and five minutes after birth, as well as complication of labor, lower gestational age at birth, and higher parity. This study demonstrates the importance of altitude and trimester specific adjustments to maternal hemoglobin levels in order to accurately diagnose anemia in pregnancy. In addition, a clear correlation is seen between maternal hemoglobin level and pregnancy outcome.

Development of aptitude at altitude

Millions of people currently live at altitudes in excess of 2500 metres, where oxygen supply is limited, but very little is known about the development of brain and behavioural function under such hypoxic conditions. We describe the physiological, cognitive and behavioural profile of a large cohort of infants (6-12 months), children (6-10 years) and adolescents (13-16 years) who were born and are living at three altitude locations in Bolivia ( approximately 500 m, approximately 2500 m and approximately 3700 m). Level of haemoglobin oxygen saturation and end-tidal carbon dioxide were significantly lower in all age groups living above 2500 metres, confirming the presence of hypoxia and hypocapnia, but without any detectable detriment to health. Infant measures of neurodevelopment and behaviour yielded comparable results across altitude groups. Neuropsychological assessment in children and adolescent groups indicated a minor reduction in psychomotor speed with increasing altitude, with no effect of age. This may result from slowing of underlying brain activity in parallel with reduced cerebral metabolism and blood flow, evidenced here by reduced cerebral blood flow velocity, particularly in the basilar artery, in children and adolescents. The proportion of European, Native American and African genetic admixture was comparable across altitude groups, suggesting that adaptation to high altitude in these children occurred in response to chronic hypoxic exposure irrespective of ethnic origin. Thus, psychomotor slowing is proposed to be an adaptive rather than a deficient trait, perhaps enabling accuracy of mental activity in hypoxic conditions.

Oxygen as a neonatal health hazard: call for détente in clinical practice

Education in oxygenation and in how oxygen is given to newborns needs to increase. Treatment with oxygen should no longer be considered proverbial and customary, regardless of our 'past experience' or consensus recommendations in clinical guidelines, since oxygen may lead to acute or chronic health effects.

CONCLUSION

Inappropriate oxygen use is a neonatal health hazard associated with aging, DNA damage and cancer, retinopathy of prematurity, injury to the developing brain, infection and others. Neonatal exposure to pure O2, even if brief, or to pulse oximetry >95% when breathing supplemental O2 must be avoided as much as possible.

Going to High Altitude with a Newborn Infant

Fetal life conditions the responses of a newborn infant to high altitude. The fetal circulation is characterized by high pulmonary vascular resistance and low pulmonary blood flow, as well as intra and extracardiac shunts that serve to route blood to and from the placenta and around the fetal lungs. At birth, rapid changes occur in the pulmonary circulation under normoxia; pulmonary vascular resistance falls, pulmonary blood flow increases dramatically, and the fetal shunts close functionally, then anatomically. Under conditions of hypoxia, the changes of circulatory transition occur more slowly, and pronounced hypoxia can cause a reversion to fetal circulatory patterns, albeit without the placenta to serve as the organ of oxygenation. Underlying medical conditions of newborn infants that combine exaggerated hypoxemia in response to high altitude hypoxia with an underlying predisposition to pulmonary hypertension can increase the likelihood of problems at high altitude. Awareness of risk factors and clinical signs of hypoxemia in newborn infants, as well as measurement of arterial oxygen saturation by pulse oximetry, can aid health professionals and parents in recognizing and preventing altitude-associated illness.

Postnatal cardiopulmonary adaptations to high altitude

Postnatal cardiopulmonary adaptations to high altitude constitute a key component of any set of responses developed to face high altitude hypoxia. Such responses are required ultimately to meet the energy demands necessary for adequate functioning at cell and organism level. After a brief insight on general and cardiopulmonary comparative studies in growing and adult organisms, differences and possible explanations for varying cardiopulmonary pathology, pulmonary artery hypertension, persistent right ventricular predominance and subacute high altitude pulmonary hypertension in different populations of children living at high altitude are discussed. Potential long-term implications of early chronic hypoxic exposure on later diseases are also presented. It is hoped that this review will help the practicing physician working at high altitude to make informed decisions concerning individual pediatric patients, specifically with regard to diagnosis and management of altitude-related cardiopulmonary pathology. Finally, plausibility and the knowledge-base of public health interventions to reduce the risks posed by suboptimal or inadequate postnatal cardiopulmonary responses to high altitude are discussed.

A Comparative Analysis of Arterial Oxygen Saturation among Tibetans And Han Born And Raised at High Altitude

This study compares resting arterial oxygen saturation as measured by pulse oximetry (Sp(O2)) among 818 Tibetans and 668 Han who were born and raised at altitudes between 3200 and 4300 m in Qinghai Province, Western China. Both Tibetans and Han show an increase in Sp(O2) values between the ages of 5 and 19 yr, and both groups show a decline after the third decade. However, mean, age-adjusted Sp(O2) values at rest do not differ significantly among growing Tibetans and Han aged 5 through 19 yr or among Tibetans and Han aged 20 through 51 yr. Therefore, the results of this study do not support the hypothesis that indigenous groups possess a superior arterial saturation while awake and at rest compared to lowlanders who have been born and raised at high altitude. Differences between adult Tibetan males and females approach statistical significance (females show higher values than males), while differences between adult Han males and females are not statistically significant. A review of the literature indicates that substantial interstudy variation exists in resting Sp(O2) values among Tibetans residing at high altitudes (between 2% and 4%, depending on the age of individuals measured) and may reflect differences in sample size, health of participants, instruments, probe location, and measurement protocols.

Growth and development of Andean high altitude residents

Growth and development under conditions of chronic hypoxia result in a different pattern of growth in Andean highlanders than in lowlanders. Growth at high altitude results in a small (1 to 4 cm) delay in linear growth, with most, if not all, of the delay probably established at or soon after birth. It also results in an enhancement of lung volumes, particularly residual volume, which is 70%-80% larger in highland than lowland children, on average, with the magnitude of the increase being positively related to age. In addition, growth and development under conditions of chronic hypoxia result in a blunted ventilatory response to hypoxia, a 4% to 5% reduction in Sa(O2), and a substantial increase in pulmonary diffusing capacity. Andean highlanders have V(O2 max) similar to that of lowlanders at low altitude, suggesting that they have successfully adapted to their hypoxic environment. It is likely that both developmental and genetic factors influence most, if not all, components of the cardiorespiratory system of Andean highlanders, but the relative importance of each is not clear.

Sustained Acclimatization in Chilean Mine Workers Subjected to Chronic Intermittent Hypoxia

Farias, Jorge G., Jorge Osorio, Gustavo Soto, Julio Brito, Patricia Siques, and Juan G. Reyes. Sustained acclimatization in Chilean mine workers subjected to chronic intermittent hypoxia. High Alt. Med. Biol. 7:302-306, 2006--We wanted to know if sea-level mine workers exposed previously to chronic intermittent hypoxia reached a steady acclimatization at 36 months under hypobaric hypoxia. An intermittently exposed group of mine workers (IE, n = 25) were subjected to submaximal exercise (100 W) at 4500 m. Their systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), and hemoglobin oxygen saturation (HbSatO(2)) were monitored. Two comparison groups of unacclimatized sea-level workers (n = 17) were studied. A nonexposed group (NE) performed 5 min of submaximal exercise at sea level. Some kind of exercise was performed both by an acutely exposed group (AE) and IE group at 4500 m. No statistical differences were found for HR, SBP, and DBP (p > 0.05) during exercise between IE and AE groups. Resting HbSatO(2) of IE (87 +/- 6%) was lower than NE (97 +/- 3%) (p < 0.05), but was higher than AE (82 +/- 4%) (p < 0.05). In the exercise condition, HbSatO(2) of IE (85 +/- 5%) was lower than NE (95 +/- 3%) (p < 0.05), but was higher than AE (76 +/- 2%) (p < 0.05). These responses were maintained through the 6 months of the study period. Thus, mine workers subjected to intermittent hypobaric condition for 3 years showed a good degree of acclimatization that was maintained through time.

Human behaviour and development under high-altitude conditions

Although we are far from a universally accepted pattern of impaired function at altitude, there is evidence indicating motor, perceptual, memory and behavioural deficits in adults. Even relatively low altitudes (2500 m) may delay reaction time, and impair motor function. Extreme altitude exposure (>5000 m) may result in more pronounced impairment that can persist after returning to the lowlands. Research into the effects of altitude exposure earlier in development is lacking by comparison. Un-acclimatized children can suffer from acute mountain sickness, and, in native populations born at altitude, subtle cognitive and behavioural deficits suggest incomplete adaptation to hypoxia. The study of neurobehavioural functioning at altitude may provide important information about the effects of clinical hypoxia on the human brain and behavioural development.

Effect of altitude on hospitalizations for respiratory syncytial virus infection

OBJECTIVE

Respiratory syncytial virus (RSV) infection is the foremost cause of serious lower respiratory tract infection in young children and infants. Because higher rates of hospitalization for bronchiolitis and pneumonia have been noted in high-altitude regions, we hypothesized that physiologic responses to altitude would predispose children to more severe illness from RSV infection. This study examined the effect of residential altitude on hospitalizations for RSV infection in Colorado from 1998 through 2002.

METHODS

A geographic information system was used to assemble data for altitude and demographic variables by zip code-tabulation areas. Data then were linked with hospital discharge data for RSV infections. Poisson regression models were developed to explore correlations between hospitalization rates and residential altitude, after adjustment for socioeconomic differences in the underlying population.

RESULTS

RSV-associated hospitalizations averaged 15.9 per 1000 infants who were younger than 1 year and 1.8 per 1000 children who were 1 to 4 years of age per season. A multivariate analysis suggested that the rate of hospitalization for RSV-specific International Classification of Diseases, Ninth Revision, Clinical Modification codes increased 25% among infants who were younger than 1 year and 53% among children who were 1 to 4 years of age for every 1000-m increase in altitude. The risk for RSV-associated hospitalization was highest at elevations above 2500 m.

CONCLUSIONS

High altitude above 2500 m is a modest predictor for RSV-associated hospitalization. Practitioners in these regions should consider additional efforts to educate parents about RSV infection and its prevention and the importance of early treatment.

Arterial oxygen saturation in healthy newborns delivered at term in Cerro de Pasco (4340 m) and Lima (150 m)

BACKGROUND

High altitude is associated with both low pulse oxygen saturation at birth and more pre-term deliveries. The present study was performed to determine pulse oxygen saturation in newborns at term in Cerro de Pasco (4340 m) and Lima (150 m) to test the hypothesis that low pulse oxygen saturation at birth at high altitudes was not observed at term deliveries.

METHODS

The present study was designed to determine pulse oxygen saturation values through 1 minute to 24 hours and values of Apgar score at 1 and 5 minutes in newborns delivered at term in Cerro de Pasco (4340 m) and Lima (150 m). Pulse oxygen saturation was recorded in 39 newborns from Cerro de Pasco (4340 m) and 131 from Lima (150 m) at 1, 2, 3, 4, 5, 10, 15, 30 minutes and 1, 2, 8 and 24 hours after delivery. Apgar score was assessed at 1 and 5 minutes after birth. Neurological score was assessed at 24 h of birth by Dubowitz exam.

RESULTS

Pulse oxygen saturation increased significantly from 1 to 15 min after birth at sea level and from 1 to 30 minutes at Cerro de Pasco. Thereafter, it increased slightly such that at 30 min at sea level and at 60 minutes in Cerro de Pasco it reached a plateau up to 24 hours after birth. At all times, pulse oxygen saturation was significantly higher at sea level than at high altitude (P < 0.01). At 1 minute of life, pulse oxygen saturation was 15% lower at high altitude than at sea level. Apgar score at 1 minute was significantly lower at high altitude (P < 0.05). Neurological score at 24 hours was also lower at high altitude than at sea level. Head circumference, and Apgar score at 5 minutes were similar at sea level and at high altitude (P:NS). Incidence of low birth-weight (<2500 g) at high altitude (5.4%) was similar to that observed at sea level (2.29%) (P:NS). Incidences of low pulse oxygen saturation (<30%), low Apgar score at first minute (<7) and low neurological score at 24 h (<19) were significantly higher at high altitude than at sea level (P < 0.0001; P < 0.0001; and P < 0.001, respectively).

CONCLUSION

From these analyses may be concluded that pulse oxygen saturation at 4340 m was significantly low despite the fact that births occurred at term. Apgar scores at first minute and neurological scores were also lower at high altitudes.

Cardiopulmonary transition in the high altitude infant

The perinatal cardiopulmonary transition at high altitude differs from that at sea level because oxygen plays a fundamental role in the developmental changes from fetus to newborn infant. Under conditions of high altitude hypoxia, arterial oxygen saturations are lower, breathing patterns and maturation of respiratory control reflexes differ, and regression of fetal characteristics of the pulmonary vasculature proceeds more slowly. Several aspects of transition vary not only with postnatal age and altitude, but also with population group, suggesting an effect of genetic adaptation on perinatal physiology. Exposure to chronic high altitude hypoxia during the perinatal transition also results in apparent lifelong alterations in respiratory reflex responses and pulmonary vasoreactivity. Disruption of the normal process of cardiopulmonary transition can result in symptomatic high altitude pulmonary hypertension. The exaggerated hypoxemia associated with acute respiratory infections in young infants still undergoing transition contributes to infant mortality at high altitude.

Oxygen saturation and heart rate in healthy school children and adolescents living at high altitude

This study was conducted to establish reference values for percent oxygen saturation of hemoglobin (SaO2, %) and heart rate (HR, bpm) in children living at high altitude (4,100 m) and to relate possible differences in the variables with ethnic origin. Healthy children from a mine-located school (Tintaya, n = 417), a nearby school (Marquiri, n = 474), and a rural Andean community (Nuñoa, n = 373) were investigated. The samples included different ethnic combinations, with the Nuñoa children having a predominant Quechua ancestry. Mean SaO2 for all ages was substantially lower in all high altitude children compared to values considered normal for sea level. Among the three samples, SaO2 was higher (91.3 +/- 2.7) and HR was lower (84.8 +/- 13.6) in Nuñoa than in Tintaya (SaO2, 89.8 +/- 2.5; HR, 91.7 +/- 14.9) and Marquiri (SaO2, 89.6 +/- 3.1; HR, 88.5 +/- 12.9) (P < 0.05). There was no sex difference and only a weak age-dependent trend for SaO2. Values considered abnormal at sea level were observed in all healthy high-altitude children. Higher SaO2 and lower HR in Nuñoa children may suggest a better degree of acclimatization to altitude.